Light-projecting device

ABSTRACT

A light-projecting device comprises an ocular optical system facing an emergent opening of a hollow pentagonal mirror. A superimpose-plate is provided in an incident opening of the hollow pentagonal mirror so that a subject image obtained through a photographing optical system is formed. The superimpose-plate is put on a focusing glass. A mark, indicated in a picture plane of the view finder, is formed on the superimpose-plate. A light source radiates an illumination light beam. A light-projecting prism reflects the illumination light beam toward the emergent opening. The light-projecting prism has a light-projecting plane. The light-projecting plane is located below the optical axis of the ocular optical system.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a light-projecting device provided for indicating a focused point, for example, in a view finder of a single-lens reflex camera.

[0003] 2. Description of the Related Art

[0004] Conventionally, there is known a single-lens reflex camera provided with a function, in which a plurality of distance-measurement points are set for an image to be photographed, and a point, which is in-focus and included in the distance-measurement points, is indicated and superimposed on a subject image in a view finder, as disclosed in Japanese Unexamined Patent Publication No. 2002-268128. Namely, a focusing glass and a superimpose-plate are superposed on each other, and disposed under a hollow pentagonal mirror, and if the number of the distance-measurement points is seven, seven small focusing marks are formed on the superimpose-plate. A light-projecting optical system is provided in a rear portion or an emergent opening of the hollow pentagonal mirror and above an ocular optical system. In a photographing operation, when any point of the distance-measurement points is in-focus, an illumination light beam is radiated from the light-projecting optical system onto the corresponding focusing mark, so that the photographer can recognize the in-focus point.

[0005] The light-projecting optical system has a light source and a light-projecting prism, which are disposed at an upper portion of the emergent opening of the hollow pentagonal mirror. Namely, the illumination light beam output from the light source is reflected on the light-projecting prism, and is directly radiated on the superimpose-plate through the emergent opening.

[0006] The illumination light beam is reflected on the roof reflecting plane and the third reflecting plane after being reflected on the superimpose-plate, and is apt to enter the ocular optical system, as ghost light. Because of this phenomenon, it sometimes happens that the view finder picture plane is not clear for the photographer, and therefore, it is preferable to remove the ghost light.

SUMMARY OF THE INVENTION

[0007] Therefore, an object of the present invention is to provide a light-projecting device in which ghost light, derived from the illumination light beam radiated on the focusing marks, is prevented from being generated.

[0008] According to the present invention, there is provided a light-projecting device for a view finder, comprising an ocular optical system, a superimpose-plate, and a light-projecting optical system.

[0009] The ocular optical system faces an emergent opening of a hollow pentagonal mirror. The superimpose-plate is provided in an incident opening of the hollow pentagonal mirror. The superimpose-plate is put on a focusing glass, on which a subject image obtained through the photographing optical system is formed. A mark, indicated in a picture plane of the view finder, is formed on the superimpose-plate. The light-projecting optical system has a light-projecting plane for projecting an illumination light beam, which is to be radiated onto the mark, into the hollow pentagonal mirror through the emergent opening. The light-projecting plane is located below the optical axis of the ocular optical system.

[0010] Further, according to the present invention, there is provided a light-projecting device for a view finder, comprising a hollow pentagonal mirror, an ocular optical system, a focusing glass, a superimpose-plate, a light source, and a light-projecting prism.

[0011] The ocular optical system faces an emergent opening of a hollow pentagonal mirror. The focusing glass is provided in an incident opening of the hollow pentagonal mirror so that a subject image obtained through a photographing optical system is formed. The superimpose-plate is put on the focusing glass. A mark, indicated in a picture plane of the view finder, is formed on the superimpose-plate. The light source radiates an illumination light beam. The light-projecting prism reflects the illumination light beam toward the emergent opening. The light-projecting prism has a light-projecting plane. The light-projecting plane is located below the optical axis of the ocular optical system.

[0012] Furthermore, according to the present invention, there is provided a light-projecting device for a view finder, comprising an ocular optical system, a superimpose-plate, and a light-projecting optical system.

[0013] The ocular optical system faces an emergent opening of a hollow pentagonal mirror. The superimpose-plate is provided in an incident opening of the hollow pentagonal mirror. The superimpose-plate is put on a focusing glass, on which a subject image obtained through the photographing optical system is formed. A mark, indicated in a picture plane of the view finder, is formed on the superimpose-plate. The superimpose-plate is inclined so that an edge, close to the photographing optical system, of the superimpose-plate is lowered. The light-projecting optical system, has a light-projecting plane for projecting an illumination light beam, which is to be radiated onto the mark, into the hollow pentagonal mirror through the emergent opening. The light-projecting plane is located beside the ocular optical system.

[0014] Still further, according to the present invention, there is provided a light-projecting device for a view finder, comprising a hollow pentagonal mirror, an ocular optical system, a focusing glass, a superimpose-plate, a light source, and a light-projecting prism.

[0015] The ocular optical system faces an emergent opening of the hollow pentagonal mirror. The focusing glass is provided in an incident opening of the hollow pentagonal mirror so that a subject image obtained through a photographing optical system is formed. The superimpose-plate is put on the focusing glass. A mark, indicated in a picture plane of the view finder, is formed on the superimpose-plate. The superimpose-plate is inclined so that an edge, close to the photographing optical system, of the superimpose-plate is lowered. The light source radiates an illumination light beam. The light-projecting prism reflects the illumination light beam toward the emergent opening. The light-projecting prism has a light-projecting plane. The light-projecting plane is located beside the ocular optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The objects and advantages of the present invention will be better understood from the following description, with reference to the accompanying drawings in which:

[0017]FIG. 1 is a sectional view showing a mirror box and a view finder optical system, to which a first embodiment of the present invention is applied, and in which a light-projecting prism is removed;

[0018]FIG. 2 is a sectional view showing the mirror box and the view finder optical system, in which an ocular optical system is removed;

[0019]FIG. 3 is a perspective view in which a hollow pentagonal mirror is viewed from the rear side;

[0020]FIG. 4 is a view showing an arrangement of focusing marks formed on a superimpose-plate or SI-plate;

[0021]FIG. 5 is a sectional view showing a light source;

[0022]FIG. 6 is a perspective view showing a disassembled focusing glass and SI-plate;

[0023]FIG. 7 is an enlarged perspective view of the SI-plate;

[0024]FIG. 8 is an enlarged plane view-showing a central portion of the SI-plate;

[0025]FIG. 9 is a cross-sectional view along a line IX-IX of FIG. 8; and

[0026]FIG. 10 is a longitudinal sectional view along a line X-X of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The present invention will be described below with reference to the embodiments shown in the drawings.

[0028]FIG. 1 and FIG. 2 are sectional views showing a mirror box and a view finder optical system of a single-lens reflex camera, FIG. 1 indicating a state in which a light-projecting prism is removed, FIG. 2 indicating a state in which an ocular optical system is removed. FIG. 3 is a perspective view in which a hollow pentagonal mirror is viewed from the rear side or a side of the ocular optical system.

[0029] A mirror box 11 has an opening 12 at the front portion thereof (i.e., left side in FIGS. 1 and 2), through which light, passing through a photographing optical system (not shown), is made incident. A hollow pentagonal mirror 21 is provided above the mirror box 11. A quick return mirror 13 is housed in the mirror box 11, to reflect light entering through the opening 12 to the hollow pentagonal mirror 21. The quick return mirror 13 is rotatably supported by a pin 14 provided above the rear portion of the mirror box 11.

[0030] A focusing glass 31, on which a subject image obtained through the photographing optical system is formed, and a superimpose-plate (i.e., SI-plate) 32, on which micro-prisms are formed, are provided in an incident opening formed at a lower portion of the hollow pentagonal mirror 21, which is disposed in the upper portion of the mirror box 11. The SI-plate 32 is put on the focusing glass 31. A focusing mark, indicated in a picture plane of the view finder, is formed on the SI-plate 32. The focusing glass 31 and the SI-plate 32 are inclined by a few degrees (e.g., about 5 degrees) in such a manner that the front edges, close to the photographing optical system, of the focusing glass 31 and the SI-plate 32, are lowered. On the other hand, the ocular optical system 23 faces an emergent opening 22 of the-hollow pentagonal opening 21. The emergent opening 22 is roughly triangular, and a photometry optical system 24 is provided at a portion close to an upper end of the emergent opening 22. Note that the photometry optical system 24 is omitted in FIG. 3.

[0031] The hollow pentagonal mirror 21 has a roof reflecting plane 41, formed at an upper portion, and a third reflecting plane 42, formed at a front portion. A light beam B1, passing through the photographing optical system and reflected on the quick return mirror 13, passes through the focusing plate 31 and the SI-plate 32, is reflected on the roof reflecting plane 41, and reaches the third reflecting plane 42. The light beam B2 reflected on the third reflecting plane 42 passes through the emergent opening 22, and enters the ocular optical system 23.

[0032] A light source 25 and a light-projecting prism 26, which form a light-projecting optical system, are provided outside the emergent opening 22. The light source 25 is disposed beside the photometry optical system 24, and close to an upper end of the emergent opening 22. The light-projecting prism 26 is disposed below the light source 25 and beside the ocular optical system 23, and directly fixed on an attaching portion 43 integrally formed on a frame of the hollow pentagonal mirror 21. The optical axis A extending between the light source 25 and the light-projecting prism 26 is approximately parallel to the plane of the emergent opening 22, and does not interfere with the optical path of the photometry optical system 24.

[0033] A light-projecting plane 26 a, or an emergent plane of the light-projecting prism 26, faces a corner of a lower portion of the emergent opening 22, and is positioned below the optical axis of the ocular optical system 23. An illumination light beam C1, output from the light source 25 to the light-projecting prism 26, is reflected on the light-projecting prism 26, and is projected from the light-projecting plane 26 a toward the emergent opening 22. The illumination light beam C1 is directed slightly upward with respect to the horizontal plane, and is led to approximately the center portion of the third reflecting plane 42 through the emergent opening 22. The illumination light beam C2 reflected on the third reflecting plane 42 is reflected on the roof reflecting plane 41, and is approximately perpendicularly radiated onto the SI-plate 32.

[0034]FIG. 4 indicates an arrangement of the focusing marks M formed on the SI-plate 32. In the embodiment, when viewing the ocular optical system 23, the photographer can observe eleven focusing marks M superposed on the subject image, in a picture plane of the view finder. The photographing optical system can focus at points corresponding to the eleven focusing marks M, with respect to the subject. When an in-focus state is obtained in a photographing operation, a focusing mark M corresponding to the in-focus point lights in red, for example. Namely, when it is sensed by an in-focus sensor that any point on the subject is in-focus, a focusing mark M corresponding to the in-focus point is illuminated by the illumination light beam C2 projected from the light source 25.

[0035] The light source 25 is provided with eleven radiating units or light emitting diodes (LEDs) 27 corresponding to the focusing marks M. Each of the LEDs 27 corresponds to one focusing mark M. Namely, illumination light beams output from the LEDs 27 are radiated on different portions of the SI-plate 32. As shown in FIG. 5, a tapered hole 29 is formed in a frame 28 of the light source 25, so that illumination light beams output from the LEDs 27 are led to the light-projecting prism 26.

[0036]FIG. 6 shows the focusing-glass 31 and the SI-plate 32, which are disassembled. A focusing glass frame 33, which is a rectangular frame, is pivotally supported by an upper end of the mirror box 11 at the rear end 34 (see FIG. 1), and has an engaging portion 35 at a front edge, which can be engaged with a predetermined portion of the mirror box 11. The focusing glass 31 is fit in the focusing glass frame 33. The SI-plate 32 is placed on the focusing glass 31 with a channel-shaped focus-adjusting washer 36 intervening therebetween. Namely, space of a predetermined size is formed between the focusing glass 31 and the SI-plate 32 by the channel-shaped focus-adjusting washer 36. The focusing glass 31, the channel-shaped focus-adjusting washer 36, and the SI-plate 32 are superposed on each other, and are supported by the focusing glass frame 33 and fixed to an upper portion of the mirror box 11.

[0037]FIG. 7 is an enlarged perspective view showing the SI-plate 32. The SI-plate 32 is a transparent member formed of a plastic material. The SI-plate 32 has a plane-parallel plate 37 and an outer frame 38 enclosing the plane-parallel plate 37. The outer frame 38 is mounted on the focus-adjusting washer 36. A rib 39 is formed on an outer surface of a short side of the outer frame 38. The plane-parallel plate 37 is inclined by an angle (1-3 degrees, for example) relative to the outer frame 38. Namely, the plane-parallel plate 37 is inclined so that an edge, close to the photographing optical system (i.e., the left side in FIGS. 1 and 2), of the SI-plate is lowered relative to the focusing glass 31. In other words, the SI-plate 32 is more inclined than the focusing glass 31.

[0038]FIG. 8 shows an enlarged view of the central portion of the SI-plate 32, when viewed from the upper side of the SI-plate 32 and when facing the SI-plate 32 from the side of the photographing optical system, and is also an enlarged view of the central portion of FIG. 4. Namely, the left side of FIG. 8 corresponds to the left side of the picture plane of the view finder.

[0039] Lots of micro-prisms 52 a, 52 b are formed to project from the lower surface of the SI-plate 32. An outline of a micro-prism is a slender trapezoid, when viewing the SI-plate 32 from an upper or lower side. The micro-prism shows a triangle in a cross-section, as described later, and a ridgeline of each of the micro-prisms 51 c, 52 c, and 53 c is parallel to the right-left (or horizontal) direction of the picture plane of the view finder. In other words, the longitudinal direction of each of the micro-prisms is coincident with the horizontal direction in the picture plane of the view finder. The micro-prisms form eleven groups, and each of the micro-prism groups 51-61 corresponds to the focusing mark M (see FIG. 4) indicated in the picture plane of the view finder. Namely, each of the focusing marks M is formed by an aggregation of a plurality of micro-prisms.

[0040] In a picture plane of the view finder, the first micro-prism group 51 is located at the leftmost side. The second, third, and fourth micro-prism groups 52, 53, and 54 are positioned at the right side of the first micro-prism group 51. The fifth, sixth, and seventh micro-prism groups 55, 56, and 57 are located at the center of all the micro-prism groups. The eighth, ninth, and tenth micro-prism groups 58, 59, and 60 are positioned at the right side of the fifth, sixth, and seventh micro-prism groups 55, 56, and 57, and the eleventh micro-prism group 61 is at the rightmost side.

[0041] Taking the second micro-prism group 52 as a typical example, the structures of the micro-prism groups 51 through 61 are described below. The second micro-prism group 52 is composed of a plurality of micro prisms, and has relatively large first micro-prisms 52 a and relatively small second micro-prisms 52 b.

[0042] The first micro-prisms 52 a are aligned horizontally in FIG. 8 in groups of three, to form four first prism rows R1. In a first prism row R1, the micro-prisms 52 a, which are adjacent, are in contact with each other. Namely, an upper side of the trapezoid of a micro-prism 52 a, positioned at the center of a row, is in contact with a lower side of the trapezoid of the micro-prism 52 a, disposed at the left side of the center micro-prism 52 a. A lower side of the trapezoid of the center micro-prism 52 a is in contact with an upper side of the trapezoid of the other micro-prism 52 a, disposed at the right side of the center micro-prism 52 a.

[0043] There are four first prism rows R1. In the space formed between the first prism rows R1 a second prism row R2 composed of a second micro-prisms 52 b is provided. The second micro-prism rows R2 are constructed by arranging the second micro-prisms 52 b horizontally in FIG. 8, in pairs. A lower side of the trapezoid of the left micro-prism 52 b is in contact with an upper side of the trapezoid of the right micro-prism 52 b.

[0044] The second micro-prism 52 b is located at a position corresponding to a place between the two first micro-prisms 52 a, adjacent to the-first prism row R1. An oblique side of the trapezoid of the second micro-prism 52 b is in contact with an end point of the lower side of the trapezoid of the first micro-prism 52 a. Similarly, an end point of the lower side of the trapezoid of the second micro-prism 52 b is in contact with an oblique side of the trapezoid of the first micro-prism 52 a. Thus, the micro-prisms 52 a and 52 b are arranged in a zigzag manner.

[0045]FIGS. 9 and 10 show the second micro-prism group 52. FIG. 9 is a cross-sectional view along line IX-IX of FIG. 8, and FIG. 10 is a longitudinal sectional view along line X-X of FIG. 8. The cross-section shape of each of the first and second micro-prisms 52 a and 52 b is approximately an isosceles triangle, so that an incident light beam radiated from the above reflects on the micro-prisms 52 a and 52 b, and returns in parallel to the incident light beam. Note that the vertical angle of the triangle of each of the micro-prisms 52 a and 52 b is approximately 90 degrees.

[0046] The ridgeline 52 c of the reflecting plane of the first micro-prism 52 a is at a slant relative to the lower surface 32 a of the SI-plate 32, as understood from FIG. 10. The slant angle α is determined in such manner that an illumination light beam C2 (see FIG. 2), radiated from the roof reflecting plane 41 of the hollow pentagonal mirror 21, is effectively received by the micro-prism 52 a. The illumination light beam C2 is radiated from a point above the light source corresponding point C3, shown in FIG. 8, to the SI-plate 32. Therefore, the angle of inclination of an illumination light beam become greater, as it separates from the light-source corresponding point C3.

[0047] Thus, regarding the inclination angle α of the ridgeline of each of the micro-prism groups, the first micro-prism group 51 is the largest. The inclination angles α of the second, third, and fourth micro-prism groups 52, 53, and 54 are equal to each other, and are smaller than that of the first micro-prism group 51. The inclination angles α of the fifth, sixth, and seventh micro-prism groups 55, 56, and 57 are equal to each other, and are smaller than those of the second, third, and fourth micro-prism groups 52, 53, and 54. The inclination angles α of the eighth, ninth, and tenth micro-prism groups 58, 59, and 60 are equal to each other, and are smaller than those of the fifth, sixth, and seventh micro-prism groups 55, 56, and 57.

[0048] The eleventh micro-prism group 61 is located at the opposite side of the ninth micro-prism 59 with respect to the light source corresponding point C3. Accordingly, the inclination angle α of the eleventh micro-prism group 61 is opposite to that of the eighth, ninth, and tenth micro-prism groups 58, 59, and 60, but is approximately the same amount as that for the eighth, ninth, and tenth micro-prism groups 58, 59, and 60.

[0049] As described above, the number of different inclination angles α of the ridgelines of the first through eleventh micro-prism groups 51 through 61, is five. The inclination angles α differ in accordance with the horizontal positions in a picture plane of the view finder, and the inclination angles α of the ridgelines of the micro-prism groups aligned in a vertical direction in the picture plane (for example, the micro-prism groups 52, 53, and 54) are the same.

[0050] Thus, on a lower surface 32 a of the SI-plate 32, the micro-prism groups 51 through 61 are formed at the positions where illumination light beams output from the light source 25 are radiated, and correspond to the focusing marks M. In a photographing operation, when the photographing optical system focuses on any point on the subject, the LED 27 (FIG. 5) corresponding to the point is lit. Due to the illumination light beam C2 (FIG. 2) output from the LED 27, the corresponding micro-prism or the focusing mark M shines in red, the photographer can recognize the focused point.

[0051] Note that, in FIG. 8, each of the second through fifth micro-prism groups 52 through 55, and the seventh through tenth micro-prism groups 57 through 60 are square shaped. The sixth micro-prism group 56 is a frame shaped. Further, the first and eleventh micro-prism groups 51 and 61 are rectangular shaped. These shapes can be changed in accordance with necessity or object.

[0052] A metal mold for forming a plastic material is used for manufacturing the SI-plate 32 having lots of micro-prisms. Namely, a tip of an edged tool is pressed on the metal mold to form the surface, by which the micro-prisms are formed. The tip of the edged tool has a triangle section, and the surface of the tip is mirror-polished. For example, a portion corresponding to the second micro-prism 52 is formed by pressing an edged tool, which has a tip having the same shape as that of the first micro-prism 52 a, on a metal mold. Namely, the corresponding portion of the first micro-prism 52 a is pressed by the edged tool to a predetermined depth, and the corresponding portion of the second micro-prism 52 b is pressed by the edged tool to a shallower depth than the first micro-prism 52 a.

[0053] As described above, there are five different kinds of inclination angle α of the micro-prisms. Therefore, five kinds of edged tools are sufficient for forming the micro-prisms. For example, regarding the second, third, and fourth micro-prisms 52, 53, and 54, since the inclination angle α is common, the same edged tool is used.

[0054] In the embodiment described above, the light source 25 is provided at an upper portion of the emergent opening 22 of the hollow pentagonal mirror 21, and the light-projecting prism 26 is provided at a lower portion of the emergent opening 22, so that the illumination light beam radiated from the light source 25 is reflected on the light-projecting prism 26, and is projected into the hollow pentagonal mirror 21 through the emergent opening 22. Therefore, in a photographing operation, when an in-focus sensor senses that any point on the subject is in-focus, and the LED 27 corresponding to the focusing point is turned ON, the illumination light beam is reflected on the third reflecting plane 42 and the roof reflecting plane 41, and is led to the SI-plate 32, so that the corresponding micro-prism group is illuminated.

[0055] Further, in the embodiment, the light-projecting plane 26 a of the light-projecting prism 26 is located below the optical axis of the ocular optical system 23, so that the illumination light beam C1 radiated from the light-projecting plane 26 a is directed slightly upward relative to the horizontal plane. Namely, the illumination light beam C1 is inclined relative to the optical axis of the ocular optical system 23 in such manner that the light beam C1 is higher at the side of the photographing optical system. Due to this, the illumination light beam is deviated toward the outside from the optical axis of the ocular optical system 23 after reflecting on the SI-plate 32. Therefore, a part of the illumination light beam is prevented from entering into the ocular optical system 23 as ghost light.

[0056] Furthermore, in the embodiment, the light-projecting plane 26 a of the light-projecting prism 26 is located beside the ocular optical system 23, and the SI-plate 32 is inclined so that an edge, close to the photographing optical system, of the IS-plate is lowered, relative to the focusing glass 31. Therefore, the illumination light beam C2 radiated on the SI-plate 32 is reflected on the SI-plate 32, and is radiated on a front portion of the roof reflecting plane 41, in comparison with a light beam entering through the photographing optical system, to deviate from the optical axis of the ocular optical system 23. Therefore, a part of the illumination light beam is prevented from entering into the ocular optical system 23 as ghost light.

[0057] Still further, in the embodiment, the SI-plate 32 is formed of a plastic material, and only the plane-parallel plate 37 is inclined relative to the outer frame 38, so that the plane-parallel plate 37 is inclined relative to the focusing glass 31 when the outer frame 38 is mounted on the focus-adjusting washer 36. Therefore, a specific adjustment of the angle of the SI-plate 32 to the focusing glass 31 is not necessary.

[0058] Although the embodiments of the present invention have been described herein with reference to the accompanying drawings, obviously many modifications and changes may be made by those skilled in this art without departing from the scope of the invention.

[0059] The present disclosure relates to subject matters contained in Japanese Patent Applications No. 2003-009357 (filed on Jan. 17, 2003) and No. 2003-009583 (filed on Jan. 17, 2003), which are expressly incorporated herein, by references, in their entirety. 

1. A light-projecting device for a view finder, comprising: an ocular optical system that faces an emergent opening of a hollow pentagonal mirror; a superimpose-plate that is provided in an incident opening of said hollow pentagonal mirror, said superimpose-plate being put on a focusing glass, on which a subject image obtained through the photographing optical system is formed, a mark, indicated in a picture plane of said view finder, being formed on said superimpose-plate; and a light-projecting optical system that has a light-projecting plane for projecting an illumination light beam which is to be radiated onto said mark, into said hollow pentagonal mirror through said emergent opening, said light-projecting plane being located below the optical axis of said ocular optical system.
 2. A light-projecting device according to claim 1, wherein said mark comprises a micro-prism formed on a surface of said superimpose-plate.
 3. A light-projecting device according to claim 1, wherein said light-projecting optical system comprises a light source radiating said illumination light beam, a light-projecting prism reflecting said illuminating light toward said emergent opening, said-light-projecting plane being an emergent plane of said light-projecting prism.
 4. A light-projecting device according to claim 3, wherein said light source is disposed close to an upper end of said emergent opening, and said light-projecting prism is disposed below said light source.
 5. A light-projecting device according to claim 3, wherein said light-projecting prism is disposed beside said ocular optical system.
 6. A light-projecting device for a view finder, comprising: a hollow pentagonal mirror; an ocular optical system that faces an emergent opening of said hollow pentagonal mirror; a focusing glass that is provided in an incident opening of said hollow pentagonal mirror so that a subject image obtained through a photographing optical system is formed; a superimpose-plate that is put on said focusing glass, a mark, indicated in a picture plane of said view finder, being formed on said superimpose-plate; a light source that radiates an illumination light beam; and a light-projecting prism that reflects said illumination light beam toward said emergent opening, said light-projecting prism having a light-projecting plane; said light-projecting plane being located below the optical axis of said ocular optical system.
 7. A light-projecting device for a view finder, comprising: an ocular optical system that faces an emergent opening of a hollow pentagonal mirror; a superimpose-plate that is provided in an incident opening of said hollow pentagonal mirror, said superimpose-plate being put on a focusing glass, on which a subject image obtained through the photographing optical system is formed, a mark, indicated in a picture plane of said view finder, being formed on said superimpose-plate, said superimpose-plate being inclined so that an edge, close to said photographing optical system, of said superimpose-plate is lowered; and a light-projecting optical system that has a light-projecting plane for projecting an illumination light beam, which is to be radiated onto said mark, into said hollow pentagonal mirror through said emergent opening, said light-projecting plane being located beside said ocular optical system.
 8. A light-projecting device according to claim 7, wherein said superimpose-plate is more inclined than said focusing glass.
 9. A light-projecting device according to claim 8, wherein said superimpose-plate is inclined by 1-3 degrees relative to said focusing glass.
 10. Alight-projecting device according to claim 7, wherein said superimpose-plate comprises a plane-parallel plate, and an outer frame enclosing said plane-parallel plate, said outer frame being mounted on a focus-adjusting washer that is provided between said superimpose-plate and said focusing glass.
 11. Alight-projecting device according to claim 7, wherein said mark comprises a micro-prism formed on a surface of said superimpose-plate.
 12. A light-projecting device according to claim 7, wherein said light-projecting optical system comprises a light source radiating said illumination light-beam, a light-projecting prism reflecting said illuminating light toward said emergent opening, said light-projecting plane being an emergent plane of said light-projecting prism.
 13. A light-projecting device; according to claim 12, wherein said light source is disposed close to an upper end of said emergent opening, and said light-projecting prism is disposed below said light source.
 14. A light-projecting device for a view finder, comprising: a hollow pentagonal mirror; an ocular optical system that faces an emergent opening of said hollow pentagonal mirror; a focusing glass that is provided in an incident opening of said hollow pentagonal mirror so that a subject image obtained through a photographing optical system is formed; a superimpose-plate that is put on said focusing glass, a mark, indicated in a picture plane of said view finder, being formed on said superimpose-plate, said superimpose-plate being inclined so that an edge, close to said photographing optical-system, of said superimpose-plate is lowered; a light source that radiates an illumination light beam; and a light-projecting prism that reflects said illumination light beam toward said emergent opening, said light-projecting prism having a light-projecting plane, said light-projecting plane being located beside said ocular optical system. 